Group 2 innate lymphoid cells suppress the pathology of neuromyelitis optica spectrum disorder.

Neuromyelitis optica spectrum disorder (NMOSD) is a severe central nervous system (CNS) autoimmune disease that primarily damages the optic nerves and spinal cord. Group 2 innate lymphoid cells (ILC2) are potent producers of type 2 cytokines that orchestrate immune and inflammatory responses. However, the role of ILC2 in CNS autoimmune diseases remains unknown. In patients with NMOSD, we identified a significant reduction of ILC2 in peripheral blood, which was correlated with disease severity. Using a mouse model of NMOSD induced by intracerebral injection of NMOSD-IgG with complement, we found CNS infiltration of ILC2 mainly expressing interleukin (IL)-5 and IL-13. The depletion of ILC2 led to increased CNS lesion volume, reduced CNS glucose metabolism, and augmented astrocyte injury and demyelination. The exacerbated NMOSD pathology was accompanied by increased accumulation of Iba1+ cells and complement activity in CNS lesions. In addition, the expansion of ILC2 using IL-33 attenuated NMO pathology. Collectively, these findings suggest a beneficial role of ILC2 in NMOSD, which deserves further investigation for future design of immune therapies to treat patients with NMOSD.

Interleukin 33 mediates hepatocyte autophagy and innate immune response in the early phase of acetaminophen-induced acute liver injury.

Despite interleukin 33 (IL-33) functions as an "alarmin" released from hepatic dead cells in response to tissue damages, the interrelationship between IL-33-mediated hepatocyte autophagy and innate immune response in the acetaminophen (APAP)-induced liver injury (AILI) process remains obscure. This study aimed to explore the regulation of IL-33 on hepatocyte autophagy and macrophage polarization after APAP challenge in vivo and vitro. We found IL-33 released from hepatic necrosis was elevated in the AILI mouse model. Blockage of IL-33 exacerbated liver injury by consuming liver-resident macrophages cells (Kupffer cells, KCs) and promoting hepatic inflammatory factors secretion, such as TNF-α, IL-6 and IL-1ß in the early phase of liver injury. Interestingly, IL-33 deficiency further activated hepatocyte autophagy and disrupted M2 macrophage polarization post-APAP challenge in vivo and vitro, which can be reversed by recombinant IL-33 treatment. Mechanistically, administration of IL-33 can directly enhance M2 polarization via PI3K/Akt signaling pathway and activate protective hepatocyte autophagy via AMPKα/mTOR signaling pathway in the AILI process. In conclusion, our data firstly demonstrates that IL-33 exerts protective effects on hepatocytes through the activation of autophagy and functions as an innate immunity regulator mediating macrophage polarization in the early phase of AILI.

Epicutaneous vaccination with protease inhibitor-treated papain prevents papain-induced Th2-mediated airway inflammation without inducing Th17 in mice.

Environmental allergen sources such as house dust mites contain proteases, which are frequently allergens themselves. Inhalation with the exogenous proteases, such as a model of protease allergen, papain, to airways evokes release and activation of IL-33, which promotes innate and adaptive allergic airway inflammation and Th2 sensitization in mice. Here, we examine whether epicutaneous (e.c.) vaccination with antigens with and without protease activity shows prophylactic effect on the Th airway sensitization and Th2-medated airway inflammation, which are driven by exogenous or endogenous IL-33. E.c. vaccination with ovalbumin restrained ovalbumin-specific Th2 airway sensitization and/or airway inflammation on subsequent inhalation with ovalbumin plus papain or ovalbumin plus recombinant IL-33. E.c. vaccination with papain or protease inhibitor-treated papain restrained papain-specific Th2 and Th9 airway sensitization, eosinophilia, and infiltration of IL-33-responsive Th2 and group 2 innate lymphoid cells on subsequent inhalation with papain. However, e.c. vaccination with papain but not protease inhibitor-treated papain induced Th17 response in bronchial draining lymph node cells. In conclusions, we demonstrated that e.c. allergen vaccination via intact skin in mice restrained even protease allergen-activated IL-33-driven airway Th2 sensitization to attenuate allergic airway inflammation and that e.c. vaccination with protease allergen attenuated the airway inflammation similar to its derivative lacking the protease activity, although the former but not the latter promoted Th17 development. In addition, the present study suggests that modified allergens, of which Th17-inducing e.c. adjuvant activity such as the protease activity was eliminated, might be preferable for safer clinical applications of the e.c. allergen administration.

Astrocyte-secreted IL-33 mediates homeostatic synaptic plasticity in the adult hippocampus.

Hippocampal synaptic plasticity is important for learning and memory formation. Homeostatic synaptic plasticity is a specific form of synaptic plasticity that is induced upon prolonged changes in neuronal activity to maintain network homeostasis. While astrocytes are important regulators of synaptic transmission and plasticity, it is largely unclear how they interact with neurons to regulate synaptic plasticity at the circuit level. Here, we show that neuronal activity blockade selectively increases the expression and secretion of IL-33 (interleukin-33) by astrocytes in the hippocampal cornu ammonis 1 (CA1) subregion. This IL-33 stimulates an increase in excitatory synapses and neurotransmission through the activation of neuronal IL-33 receptor complex and synaptic recruitment of the scaffold protein PSD-95. We found that acute administration of tetrodotoxin in hippocampal slices or inhibition of hippocampal CA1 excitatory neurons by optogenetic manipulation increases IL-33 expression in CA1 astrocytes. Furthermore, IL-33 administration in vivo promotes the formation of functional excitatory synapses in hippocampal CA1 neurons, whereas conditional knockout of IL-33 in CA1 astrocytes decreases the number of excitatory synapses therein. Importantly, blockade of IL-33 and its receptor signaling in vivo by intracerebroventricular administration of its decoy receptor inhibits homeostatic synaptic plasticity in CA1 pyramidal neurons and impairs spatial memory formation in mice. These results collectively reveal an important role of astrocytic IL-33 in mediating the negative-feedback signaling mechanism in homeostatic synaptic plasticity, providing insights into how astrocytes maintain hippocampal network homeostasis.

STING activation in alveolar macrophages and group 2 innate lymphoid cells suppresses IL-33-driven type 2 immunopathology.

2'3'-cGAMP is known as a nonclassical second messenger and small immune modulator that possesses potent antitumor and antiviral activities via inducing the stimulator of IFN genes-mediated (STING-mediated) signaling pathway. However, its function in regulating type 2 immune responses remains unknown. Therefore, we sought to determine a role of STING activation by 2'3'-cGAMP in type 2 inflammatory reactions in multiple mouse models of eosinophilic asthma. We discovered that 2'3'-cGAMP administration strongly attenuated type 2 lung immunopathology and airway hyperreactivity induced by IL-33 and a fungal allergen, Aspergillus flavus. Mechanistically, upon the respiratory delivery, 2'3'-cGAMP was mainly internalized by alveolar macrophages, in which it activated the STING/IFN regulatory factor 3/type I IFN signaling axis to induce the production of inhibitory factors containing IFN-α, which blocked the IL-33-mediated activation of group 2 innate lymphoid (ILC2) cells in vivo. We further demonstrated that 2'3'-cGAMP directly suppressed the proliferation and function of both human and mouse ILC2 cells in vitro. Taken together, our findings suggest that STING activation by 2'3'-cGAMP in alveolar macrophages and ILC2 cells can negatively regulate type 2 immune responses, implying that the respiratory delivery of 2'3'-cGAMP might be further developed as an alternative strategy for treating type 2 immunopathologic diseases such as eosinophilic asthma.

An Autocrine Circuit of IL-33 in Keratinocytes Is Involved in the Progression of Psoriasis.

IL-33 is constitutively expressed in the skin. Psoriasis is a common skin inflammatory disease. The roles of IL-33 in psoriasis have not been well-elucidated. We identified that keratinocytes (KCs) are the predominant cells expressing IL-33 and its receptor, suppression of tumorigenicity 2, in the skin. KCs actively released IL-33 on psoriasis inflammatory stimuli and induced psoriasis-related cytokine, chemokine, and inflammatory molecules genes transcription in KCs in an autocrine manner. IL-33‒specific deficiency in KCs ameliorated imiquimod-induced psoriatic dermatitis. In addition, intradermal injection of recombinant IL-33 alone induced psoriasis-like dermatitis, which is attributed to the transcriptional upregulation of genes enriched in IL-17, TNF, and chemokine signaling pathway in KCs on recombinant IL-33 stimulation. Our data demonstrate that the autocrine circuit of IL-33 in KCs promotes the progression of psoriatic skin inflammation, and IL-33 is a potential therapeutic target for psoriasis.

Characterization of immune responses and the lung transcriptome in a murine model of IL-33 challenge.

IL-33 induces airway inflammation and hyper-responsiveness in respiratory diseases. Although defined as a therapeutic target, there are limited studies that have comprehensively investigated IL-33-mediated responses in the lungs in vivo. In this study, we characterized immunological and physiological responses induced by intranasal IL-33 challenge, in a mouse model. We identified specific cytokines, IL-4, IL-5, IL-6, IL-10, IP-10 and MIP1-α, that are increased in bronchoalveolar lavage and lung tissues by IL-33. Using transcriptomics (RNA-Seq) we demonstrated that 2279 transcripts were up-regulated and 1378 downregulated (≥ 2-fold, p < 0.01) in lung tissues, in response to IL-33. Bioinformatic interrogation of the RNA-Seq data was used to predict biological pathways and upstream regulators involved in IL-33-mediated responses. We showed that the mRNA and protein of STAT4, a predicted upstream regulator of IL-33-induced transcripts, was significantly enhanced in the lungs following IL-33 challenge. Overall, this study provides specific IL-33-induced molecular targets and endpoints that can be used as a resource for in vivo studies, e.g. in preclinical murine models examining novel interventions to target downstream effects of IL-33.

Graft IL-33 regulates infiltrating macrophages to protect against chronic rejection.

Alarmins, sequestered self-molecules containing damage-associated molecular patterns, are released during tissue injury to drive innate immune cell proinflammatory responses. Whether endogenous negative regulators controlling early immune responses are also released at the site of injury is poorly understood. Herein, we establish that the stromal cell-derived alarmin interleukin 33 (IL-33) is a local factor that directly restricts the proinflammatory capacity of graft-infiltrating macrophages early after transplantation. By assessing heart transplant recipient samples and using a mouse heart transplant model, we establish that IL-33 is upregulated in allografts to limit chronic rejection. Mouse cardiac transplants lacking IL-33 displayed dramatically accelerated vascular occlusion and subsequent fibrosis, which was not due to altered systemic immune responses. Instead, a lack of graft IL-33 caused local augmentation of proinflammatory iNOS+ macrophages that accelerated graft loss. IL-33 facilitated a metabolic program in macrophages associated with reparative and regulatory functions, and local delivery of IL-33 prevented the chronic rejection of IL-33-deficient cardiac transplants. Therefore, IL-33 represents what we believe is a novel regulatory alarmin in transplantation that limits chronic rejection by restraining the local activation of proinflammatory macrophages. The local delivery of IL-33 in extracellular matrix-based materials may be a promising biologic for chronic rejection prophylaxis.

IL-33/ST2 axis is involved in disease progression in the spleen during Leishmania donovani infection.

BACKGROUND: During infection with Leishmania donovani, parasite control is linked to the systemic Th1 immune response, but in infected organs (liver, spleen and bone marrow), the response differs according to the micro-environment. The pleiomorphic cytokine interleukin-33 (IL-33) exerts various roles during infection, either protective or detrimental. In this study, we explored the role of IL-33 in the outcome of Leishmania infection in the spleen. METHODS: We used several mouse models, on BALB/c and C57BL/6 (B6) backgrounds, infected with L. donovani and sacrificed at 15, 30 or 60 days after infection and characterized mRNA expression of immune markers, immune cell populations, histological response, and parasite loads. RESULTS: During infection IL-33 and ST2 mRNA increased in parallel in the spleen of wild type (wt) animals and paralleled the immunodetection of ST2+ and IL-33+ cells; their expression was twice as high in BALB/c, compared to B6 mice. Mice treated with twice-weekly injections of rIL-33 had higher splenic parasite burdens on D15 (BALB/c) or on D60 (B6). In BALB/c, IL-33 treatment led to immune exhaustion with abolition of Th1 cytokine expression (IFN-γ and IL-12) in the spleen and higher serum levels of Th2 cytokines (IL-4, IL-5 and IL-13). In B6, IL-33 treatment induced the Treg cell pathway with a dramatic increase of FoxP3 mRNA induction and expression on tissue sections. IL-33-KO mice had lower parasite loads and a higher Th1 response than their wt counterparts. CONCLUSIONS: IL-33 appears as a factor of aggravation of the disease in the spleen tissue of mice infected with L. donovani.

IL-33 induces type-2-cytokine phenotype but exacerbates cardiac remodeling post-myocardial infarction with eosinophil recruitment, worsened systolic dysfunction, and ventricular wall rupture.

Myocardial infarction (MI) is the leading cause of mortality worldwide. Interleukin (IL)-33 (IL-33) is a cytokine present in most cardiac cells and is secreted on necrosis where it acts as a functional ligand for the ST2 receptor. Although IL-33/ST2 axis is protective against various forms of cardiovascular diseases, some studies suggest potential detrimental roles for IL-33 signaling. The aim of the present study was to examine the effect of IL-33 administration on cardiac function post-MI in mice. MI was induced by coronary artery ligation. Mice were treated with IL-33 (1 µg/day) or vehicle for 4 and 7 days. Functional and molecular changes of the left ventricle (LV) were assessed. Single cell suspensions were obtained from bone marrow, heart, spleen, and peripheral blood to assess the immune cells using flow cytometry at 1, 3, and 7 days post-MI in IL-33 or vehicle-treated animals. The results of the present study suggest that IL-33 is effective in activating a type 2 cytokine milieu in the damaged heart, consistent with reduced early inflammatory and pro-fibrotic response. However, IL-33 administration was associated with worsened cardiac function and adverse cardiac remodeling in the MI mouse model. IL-33 administration increased infarct size, LV hypertrophy, cardiomyocyte death, and overall mortality rate due to cardiac rupture. Moreover, IL-33-treated MI mice displayed a significant myocardial eosinophil infiltration at 7 days post-MI when compared with vehicle-treated MI mice. The present study reveals that although IL-33 administration is associated with a reparative phenotype following MI, it worsens cardiac remodeling and promotes heart failure.

Lipid-Droplet Formation Drives Pathogenic Group 2 Innate Lymphoid Cells in Airway Inflammation.

Innate lymphoid cells (ILCs) play an important role in the control and maintenance of barrier immunity. However, chronic activation of ILCs results in immune-mediated pathology. Here, we show that tissue-resident type 2 ILCs (ILC2s) display a distinct metabolic signature upon chronic activation. In the context of allergen-driven airway inflammation, ILC2s increase their uptake of both external lipids and glucose. Externally acquired fatty acids are transiently stored in lipid droplets and converted into phospholipids to promote the proliferation of ILC2s. This metabolic program is imprinted by interleukin-33 (IL-33) and regulated by the genes Pparg and Dgat1, which are both controlled by glucose availability and mTOR signaling. Restricting dietary glucose by feeding mice a ketogenic diet largely ablated ILC2-mediated airway inflammation by impairing fatty acid metabolism and the formation of lipid droplets. Together, these results reveal that pathogenic ILC2 responses require lipid metabolism and identify ketogenic diet as a potent intervention strategy to treat airway inflammation.

Interleukin-33 pretreatment promotes metastatic growth of murine melanoma by reducing the cytotoxic capacity of CD8+ T cells and enhancing regulatory T cells.

Interleukin-33 (IL-33) regulates innate and acquired immune response to pathogens, self-antigens and tumors. IL-33 effects on tumors depend on the dose and mode of administration along with the type of malignancy. We studied the effects of IL-33 on the development of primary and metastatic melanoma induced by B16-F1 cell line in C57BL/6 mice. Intraperitoneally applied IL-33 restricts primary tumor growth. When administered intranasally 3 days prior to the intravenous injection of the tumor cells, IL-33 promoted growth of B16-F1 melanoma metastases, while B16-F10 gave massive metastases independently of IL-33. To mimic natural dissemination, we next used a limited number (5 × 104) of B16-F1 cells intravenously followed by application of IL-33 intraperitoneally. IL-33 increased the size of metastases (10.96 ± 3.96 mm2) when compared to the control group (0.86 ± 0.39 mm2), without changing incidence and number of metastases. IL-33 increased expression of ST2 on both tumor and immune cells in metastases. Also, IL-33 enhanced eosinophils and anti-tumor NK cells in the lung. The striking finding was reduced cytotoxicity of CD8+ T cells derived from metastatic lung of IL-33 injected mice. IL-33 reduced the percentage of TNF-α+ and IFN-γ+ CD8+ T cells while increasing the frequency of CD8+ T cells that express inhibitory molecules (PD-1, KLRG-1 and CTLA-4). There was a significant accumulation of CD11b+Gr-1+ myeloid suppressor cells and FoxP3+, IL-10+ and CTLA-4+ regulatory T cells in the metastatic lung of IL-33 injected mice. The relevance of IL-33 for melanoma metastases was also documented in a significantly increased level of serum IL-33 in stage III melanoma patients.

Adjuvantic cytokine IL-33 improves the protective immunity of cocktailed DNA vaccine of ROP5 and ROP18 against toxoplasma gondii infection in mice.

Toxoplasma gondii is a threat for immunocompromized individuals, and no treatment is available for enhancing immunity against infection. Molecular adjuvants may improve the efficacy of DNA vaccine-induced T cell immunity. Here, we report that cocktailed DNA immunization with ROP5 and ROP18 boosted immune responses induced by a single DNA immunization with ROP5 or ROP18, but also that co-administration of molecular adjuvant IL-33 enhanced immune efficacy induced by this cocktailed DNA vaccination. These improved immune responses were characterized by higher Toxoplasma-specific IgG2a titers, Th1 responses associated with the production of IFN-γ, IL-2, IL-12, as well as cell-mediated activity with higher frequencies of CD8+ and CD4+ T cells. More importantly, this enhanced immunity has the ability to confer remarkable protection against a high dose lethal challenge of the T. gondii RH strain and thus against chronic infection with the T. gondii PRU strain. These data show that IL-33 is a promising immunoadjuvant to facilitate humoral as well as cellular immunity in a vaccine setting against T. gondii, and suggest that it should be evaluated in strategies against other apicomplexan parasites.

TITLE: La cytokine IL-33 utilisée comme adjuvant améliore l'immunité protectrice du vaccin à cocktail d'ADN de ROP5 et ROP18 contre l'infection à Toxoplasma gondii chez la souris. ABSTRACT: Toxoplasma gondii est une menace pour les individus immunodéprimés et aucun traitement n'est disponible pour renforcer l'immunité contre l'infection. Les adjuvants moléculaires peuvent améliorer l'efficacité de l'immunité des cellules T induite par un vaccin à ADN. Ici, nous rapportons que l'immunisation par le cocktail d'ADN de ROP5 et ROP18 a stimulé les réponses immunitaires induites par une seule immunisation par l'ADN de ROP5 ou ROP18, mais aussi que la co-administration de l'adjuvant moléculaire IL-33 a amélioré l'efficacité immunitaire induite par cette vaccination par cocktail d'ADN. Ces réponses immunitaires améliorées ont été caractérisées par des titres d'IgG2a spécifiques à Toxoplasma plus élevés, des réponses Th1 associées à la production d'IFN-γ, IL-2, IL-12 ainsi qu'une activité à médiation cellulaire où les fréquences des cellules T CD8+ et CD4+ étaient plus élevées. Plus important encore, cette immunité renforcée a la capacité de conférer une protection remarquable contre une provocation létale par haute dose de la souche RH de T. gondii et donc contre une infection chronique par la souche PRU de T. gondii. Ces données montrent qu'IL-33 est un immunoadjuvant prometteur pour faciliter l'immunité humorale et cellulaire dans un contexte de vaccination contre T. gondii et suggèrent qu'il devrait être évalué dans des stratégies contre d'autres parasites apicomplexes.

Isolation, Culture, and Induction of Plasticity in ILC2s.

Innate lymphoid cells (ILCs) are lymphocytes with critical roles in homeostasis, inflammation, and immunity to pathogens. ILCs are rare relative to other immune cell populations and are primarily defined by lack of expression of markers associated with other immune cell lineages and are predominantly found in mucosal tissues like the gut, lung and skin. They are classified into distinct subsets, ILC1, ILC2, and ILC3, which mirror subsets of CD4+ helper T cells. ILC subsets have distinct cytokine and transcription factor profiles which align with their biological functions, although recently it has emerged that ILC subsets are not phenotypically fixed and exhibit considerable heterogeneity and plasticity in different contexts. Here, we describe protocols for the maintenance, expansion, and induction of plasticity in mouse and human ILC2s. The resulting cells can be used for molecular interrogation of ILC function and biology, both in vivo and in vitro.

The Prostaglandin D2 Receptor CRTH2 Promotes IL-33-Induced ILC2 Accumulation in the Lung.

Group 2 innate lymphoid cells (ILC2s) are rare innate immune cells that accumulate in tissues during allergy and helminth infection, performing critical effector functions that drive type 2 inflammation. ILC2s express ST2, the receptor for the cytokine IL-33, and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), a receptor for the bioactive lipid prostaglandin D2 (PGD2). The IL-33-ST2 and the PGD2-CRTH2 pathways have both been implicated in promoting ILC2 accumulation during type 2 inflammation. However, whether these two pathways coordinate to regulate ILC2 population size in the tissue in vivo remains undefined. In this study, we show that ILC2 accumulation in the murine lung in response to systemic IL-33 treatment was partially dependent on CRTH2. This effect was not a result of reduced ILC2 proliferation, increased apoptosis or cell death, or differences in expression of the ST2 receptor in the absence of CRTH2. Rather, data from adoptive transfer studies suggested that defective accumulation of CRTH2-deficient ILC2s in response to IL-33 was due to altered ILC2 migration patterns. Whereas donor wild-type ILC2s preferentially accumulated in the lungs compared with CRTH2-deficient ILC2s following transfer into IL-33-treated recipients, wild-type and CRTH2-deficient ILC2s accumulated equally in the recipient mediastinal lymph node. These data suggest that CRTH2-dependent effects lie downstream of IL-33, directly affecting the migration of ILC2s into inflamed lung tissues. A better understanding of the complex interactions between the IL-33 and PGD2-CRTH2 pathways that regulate ILC2 population size will be useful in understanding how these pathways could be targeted to treat diseases associated with type 2 inflammation.

Endogenous IL-33 and Its Autoamplification of IL-33/ST2 Pathway Play an Important Role in Asthma.

IL-33 and its receptor ST2 are contributing factors to airway inflammation and asthma exacerbation. The IL-33/ST2 signaling pathway is involved in both the onset and the acute exacerbations of asthma. In this study, we address the role of endogenous IL-33 and its autoamplification of the IL-33/ST2 pathway in Ag-dependent and Ag-independent asthma-like models. Wild-type, IL-33 knockout, ST2 knockout mice were either intratracheally administrated with 500 ng of rIL-33 per day for four consecutive days or were sensitized and challenged with OVA over 21 d. In wild-type mice, IL-33 or OVA induced similar airway hyperresponsiveness and eosinophilic airway inflammation. IL-33 induced its own mRNA and ST2L mRNA expression in the lung. IL-33 autoamplified itself and ST2 protein expression in airway epithelial cells. OVA also induced IL-33 and ST2 protein expression. In IL-33 knockout mice, the IL-33- and OVA-induced airway hyperresponsiveness and eosinophilic airway inflammation were both significantly attenuated, whereas IL-33-induced ST2L mRNA expression was preserved, although no autoamplification of IL-33/ST2 pathway was observed. In ST2 knockout mice, IL-33 and OVA induced airway hyperresponsiveness and eosinophilic airway inflammation were both completely diminished, and no IL-33/ST2 autoamplification was observed. These results suggest that endogenous IL-33 and its autoamplification of IL-33/ST2 pathway play an important role in the induction of asthma-like phenotype. Thus an intact IL-33/ST2 pathway is necessary for both Ag-dependent and Ag-independent asthma-like mouse models.

Interleukin-33 activates and recruits natural killer cells to inhibit pulmonary metastatic cancer development.

Increasing evidence suggests that IL-33 plays an important role in regulating tumor development. However, conflicting results, obtained from numerous studies, have highlighted the divergent functions of IL-33. The detailed mechanisms by which IL-33 modulates tumor development merit further investigation. Here, we report that IL-33 administration can effectively inhibit the development of pulmonary metastasis of breast cancer in a mouse. In our model, IL-33 promotes the production of TNF-α by macrophages, which increases IL-33 specific receptor (ST2) expression on natural killer (NK) cells and is pivotal in IL-33-induced NK cell activation. IL-33 treatment also facilitates the production of CCL5 in the lung by eosinophils and CD8+ T cells, which mediates the recruitment of NK cells to the tumor microenvironment. The systemic activation and local recruitment of NK cells result in potent tumor rejection in the lung. Our study reports a novel mechanism for the IL-33-meditated suppression of metastatic cancer and provides potential therapeutic strategies for targeting metastatic tumor.

Nociceptor Interleukin 33 Receptor/ST2 Signaling in Vibration-Induced Muscle Pain in the Rat.

Occupational exposure to mechanical vibration can produce the hand-arm vibration syndrome (HAVS), whose most disabling symptom is persistent muscle pain. Unfortunately, the pathophysiology of HAVS pain is still poorly understood, precluding the development of mechanism-based therapies. Since interleukin 33 (IL-33) is essential for inflammation and recovery that follows skeletal muscle injury, we explored its role in muscle pain in a model of HAVS, in adult male rats. Concomitant to mechanical hyperalgesia, an increase in IL-33 in the ipsilateral gastrocnemius muscle was observed 24 hours after vibration. A similar hyperalgesia was produced by intramuscular injection of recombinant rat IL-33 (rrIL-33, 10-300 ng). Intrathecal administration of an oligodeoxynucleotide antisense to IL-33R/ST2 mRNA decreased the expression of ST2 in DRG and attenuated both rrIL-33 and vibration-induced mechanical hyperalgesia. Together these data support the suggestion that IL-33 plays a central role in vibration-induced muscle pain by action, at least in part, on skeletal muscle nociceptors. PERSPECTIVE: Our findings provide evidence of the contribution of IL-33, acting on its canonical receptor, in nociceptors, to muscle pain induced by ergonomic vibration. This suggests that targeting IL-33/ST2 signaling may be a useful strategy for the treatment of muscle pain in HAVS.

Brain Foxp3+ regulatory T cells can be expanded by Interleukin-33 in mouse ischemic stroke.

BACKGROUND: Regulatory T (Treg) cells are known as immune regulators to decrease infarct volume and improve outcomes after ischemic stroke. Thus, the strategies for increasing Treg cells in ischemic brain may have the beneficial effects on stroke. In this study, we aim to examine the effect of Interleukin-33 (IL-33) on Treg cell expansion in mouse model of ischemic stroke. METHODS: Mice were subjected to 30 min of middle cerebral artery occlusion (MCAO) followed by 24 h, 48 h of 72 h of reperfusion. Recombinant mouse IL-33 (2 µg) was pre-treated intracerebroventricularly at 30 min prior to MCAO. The percentage of Treg cells in ischemic brain, related cytokines and transcription factors, the levels of ST2 receptor, amphiregulin (AREG), and epidermal growth factor receptor (EGFR) were measured. RESULTS: IL-33 treatment can increase the number of Foxp3+ Treg cells in the ischemic brain and the levels of IL-10 and TGF- ß1 in serum and brain tissues at MCAO 48 h and 72 h, but not at MCAO 24 h. In the Treg cells separated from ischemic brain tissue following MCAO treated by IL-33, the expression level of ST2 receptor was up-regulated. In addition, IL-33 may increase the mRNA level of transcription factor Foxp3. Correspondingly, IL-33 treatment also elevated the levels of AREG and EGFR at MCAO 48 h and 72 h. CONCLUSION: We speculated that intracerebroventricular IL-33 can activate the downstream Foxp3 via ST2 receptor to increase Treg proportions in the ischemic brain. The elevated Treg cells produce AREG to activate EGFR located in neurons, which contribute to better outcomes.

Resveratrol inhibits IL-33-mediated mast cell activation by targeting the MK2/3-PI3K/Akt axis.

Interleukin-33 (IL-33)/ST2-mediated mast cell activation plays important roles in the pathophysiology of allergic diseases. Hence, pharmacologically targeting the IL-33/ST2 pathway in mast cells could help to treat such diseases. We found that resveratrol inhibits IL-33/ST2-mediated mast cell activation. Resveratrol suppressed IL-33-induced IL-6, IL-13, and TNF-α production in mouse bone marrow-derived mast cells (BMMCs), mouse fetal skin-derived mast cells, and human basophils. Resveratrol also attenuated cytokine expression induced by intranasal administration of IL-33 in mouse lung. IL-33-mediated cytokine production in mast cells requires activation of the NF-κB and MAPK p38-MAPK-activated protein kinase-2/3 (MK2/3)-PI3K/Akt pathway, and resveratrol clearly inhibited IL-33-induced activation of the MK2/3-PI3K/Akt pathway, but not the NF-κB pathway, without affecting p38 in BMMCs. Importantly, resveratrol inhibited the kinase activity of MK2, and an MK2/3 inhibitor recapitulated the suppressive effects of resveratrol. Resveratrol and an MK2/3 inhibitor also inhibited IgE-dependent degranulation and cytokine production in BMMCs, concomitant with suppression of the MK2/3-PI3K/Akt pathway. These findings indicate that resveratrol inhibits both IL-33/ST2-mediated and IgE-dependent mast cell activation principally by targeting the MK2/3-PI3K/Akt axis downstream of p38. Thus, resveratrol may have potential for the prevention and treatment of broad ranges of allergic diseases.